1. Field of the Invention
The present invention relates winch mechanisms, and in particular to a dual drive winch mechanism and a maintenance apparatus for use in servicing components of a nuclear reactor vessel, such as a control rod drive mechanism (CRDM), employing such a winch mechanism.
2. Related Art
In a Boiling Water Reactor (BWR) type nuclear reactor, a number control blades are provided within the reactor vessel, each control blade being positioned between a number of (e.g., four) nuclear fuel bundles. The power output of a BWR is controlled by the elevation position of the control blades within the fuel bundles. The position of each control blade is controlled by a control rod drive mechanisms (CRDM), which selectively raises and lowers the control blade within the BWR vessel.
At times, problems may arise with the operation of a CRDM. Some problems are severe and require replacement of the entire CRDM, which is an involved and time consuming process. Certain problems, however, such as leaking from the CRDM bolt-in location at the bottom of the reactor vessel, are less severe and merely require visual inspection and/or replacement of a minor part, such as an O-ring. In these less severe instances, it is only necessary to lower the CRDM to a position below the reactor vessel so that it can be inspected and/or so the problem part can be fixed or removed and replaced.
There is thus a need for an apparatus that simplifies and facilitates the lowering of CRDMs or other components in nuclear reactor vessels such as BWRs in order to facilitate inspection and/or maintenance of such components.